This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Secretory phospholipase A2 (sPLA2) binds to lipid bilayers and catalyzes hydrolysis of phospholipids. Normally, cells resist the enzyme's action, but they become susceptible during apoptosis or trauma. The focus of our research group is to understand what physical changes occur in the membranes of eukaryotic cells when they are traumatized by elevated intracellular calcium or induced into apoptosis by various means. The purpose is to understand the relationship between membrane structure and cell death and between membrane structure and the action of phospholipase A2. The fluorescence of membrane probes such as laurdan and patman are studied by two-photon microscopy to separate changes occuring at the plasma membrane from those that pertain to internal membranes. Moreover, these techniques allow us to identify the lateral spatial distribution of membrane properties and their relationship to apoptosis and enzyme activity. In the past, the work has been confined to static measurements. Plans are in place to begin using FCS to assess potential changes in the dynamics of membrane properties during apoptosis and trauma.